This post has been updated since it was first posted in August 2012.
The vast majority of people can’t tell a dull knife from a sharp knife. People automatically assume that if a knife can cut, it’s sharp.
Unfortunately, that’s not always the case.
A dull knife will usually cut, but it requires much more force and energy than if you’re cutting with a truly sharp knife. So how can you tell if a knife is truly sharp? Here are a few ways to determine the sharpness of a blade.
Let us know your sharpness tests in the comments.
1. The Paper Test
Probably the most tried and true method is the good ol’ fashioned paper test. Grab a piece of paper, hold it between your fingers, and slide the knife downward. If it’s sharp, it will cleanly and easily slice the paper with just the weight of the knife. If it’s dull, it will usually be ragged or slip right off. This test also allows you to find any jagged or missed spots if you cut the whole length of the edge on a single stroke.
For an even better test of a blade’s sharpness, use a piece of magazine paper. Paper from a magazine is exceptionally thin and slick, which makes it even more difficult for a knife to slice through. According to Mike Vellekamp (who used to work at Spyderco before his current venture of V Nives), Sal Glesser used to make them use paper from National Geographic magazines. Phone book paper is an even tougher test, and toilet paper is the toughest.
Yet another variation fo the paper test is to fold the paper in half so it has a rounded edge. Cut the paper along the rounded edge and if it’s sharp, it will catch and cut the page.
Here’s a good clip from the legendary Bob Kramer on the paper test.
2. The Shaving Test
If you’ve ever watched knife reviews on YouTube, you’re probably familiar with the next test. It involves running the knife along your hair (usually your arm hair) and watching the little hairs get lopped off as the blade comes gliding through. Any hairs that fold under will indicate that the blade is not up to snuff.
Our friend Mike over at Cutler Road was kind enough to write a post for us detailing the best way to sharpen your knives. You can find more of his tips on his blog.
The majority of factory-sharpened knives come with a relatively steep bevel angle of approximately 25 degrees. This gives them an acceptably sharp edge, which retains its sharpness with considerable use, and ultimately keeps the consumer happy.
Improvements can be made to the sharpness of most factory-finished knives by decreasing the angle of the bevel edge slightly. Having a shallower angle will give a sharper edge; the downside is the edge will become blunt more quickly.
Machetes and axes have the steepest angle at approximately 35 degrees. A cut throat razor, at the other end of the scale, is approximately 15 degrees. An angle of 20 degrees is a very good compromise between sharpness and edge retention for pocket knives, tactical knives, and hunting knives.
We’ve talked a lot on this blog about sharpening straight-edged knives, but we haven’t focused much on serrated blades. While we always encourage those with serrated knives to get them sharpened professionally or by the manufacturer, it is possible to sharpen one yourself. You just have to know what you’re doing.
For a straight-edged blade, you would take a sharpening stone and simply run the knife across it, but doing that with a serrated knife will only grind off the serrations. This might give the blade a specious and temporary feeling of sharpness, but it’s very bad for the blade and you should avoid it at all cost.
Instead, you will need a sharpening rod—either made from steel or ceramic. The size you get is really important, but it also depends on the size of the serrations. If you’re using a large cooking knife with wide serrations, opt for something like the DMT Ceramic Steel. For most pocket knives with small serrations, go for the DMT Diafold Serrated Sharpener. This works with made types of small serrations because the rod tapers down at the end, so it fits various sizes.
Today, the Florida-Times Union ran a great piece about an experienced and weathered knife sharpener who runs a transient business along the highway.
Phil Vanderhoof is a 59-year-old free spirit that pedals his business across state lines. That’s right pedals. His business (and really, his life) is a small trailer with a sign advertising “Phil’s Knife Sharpening” that he attaches to his bicycle.
In the trailer is a hand-turned grinding wheel he estimates is about 75 years old. He also carries a variety of oil stones to do some of the finer work.
Despite having done this for more than 20 years, he didn’t have any professional training sharpening knives, but learned a few tricks and techniques in the Boy Scouts and the Marines. He was good enough that people kept stopping him on the side of the road on his bike to sharpen their knives. So, he decided to simply attach a sign and set up shop wherever he wanted.
The great thing about his business is that he runs a great bargain. Most knives cost between $2 and $5 while a handful of swords might run you about $30.
These are just two examples of survival situations where a dull knife simply won’t cut it, literally and figuratively. In many survival situations, knives become dull from overuse, and there are no sharpening tools available.
If you ever find yourself stranded in the wilderness, here are some things you can do to sharpen and hone your knife.
There are a ton of sharpening stone options out there, but if you’re just starting out, then ceramic stones are a a pretty good bet, as they don’t need any lubricant. An Arkansas Stone or a Diamond Bench Stone are also two good basic models to go with.
Depending on what sort of stone you’ve chosen, a lubricant might be necessary. Many stones are designed to be used with a certain sort of lubricant, so it’s important to do some research and see what sort of lubricant your sharpening stone may need.
What to Do
Place your stone in one hand and put your knife on the flat side of the stone. Then, push the knife forward at an angle, approximately fifteen to twenty degrees off the stone.You should hear a smooth, grating sound as you push it forward. Work the knife back and forth between 3 and 5 times. Flip the knife over and sharpen the other side as well.
It’s a pretty easy process, but best explained via a visual aid, which is why I’ve included this totally strange video of a 13-year old knife wizard showing how it’s done. Enjoy and have a great Labor Day!